1. Field of the Invention
The present invention relates to an electrode for a lithium secondary battery, and a lithium secondary battery.
2. Description of the Related Art
In recent years, a lithium secondary battery, which uses a non-aqueous electrolyte and performs charge/discharge by transfer of lithium ions between a positive electrode and a negative electrode, has been utilized as one of new-type secondary batteries with high output and high energy density.
Silicon is a material that is capable of occluding lithium by forming an alloy with lithium. Due to the large theoretical capacity, silicon is attracting attention as a material for an electrode of a lithium secondary battery, with which improvement in energy density can be sought. However, there has been a problem in that an electrode using silicon as an active material is inferior to a carbon material such as graphite in terms of cycle characteristics. One of the causes of this is considered as follows. Since expansion and shrinkage of the active material during charge/discharge are large, the active material is pulverized by stress generated due to the expansion and shrinkage, or is released from a current collector, leading to reduction in current collectability.
The present inventors made the following finding: favorable cycle characteristics are exhibited in such a manner that, in an electrode produced by depositing an amorphous silicon thin film or the like on a current collector such as a copper foil by the CVD method or sputtering method, a slit is formed in the direction of the thin film thickness due to charge/discharge, and the thin film is then separated along the slit into columnar form (International Publication pamphlet No. 01/31720, etc.).
When the electrode is produced by formation of a thin film by the CVD method or sputtering method, it is necessary to keep the inside of a device vacuum, and when the electrodes are to be produced in large quantities, a large-sized vacuum device is required.